The present invention relates to a cannula for use in the medical field and particularly relates to a cannula useful with a syringe for penetrating membranes or septums, pre-slit or non-pre-slit, as commonly used in medications vials, intravenous bags, access ports and the like. Such penetration allows for aspiration or injection from or into a wide variety of containers.
Syringes used in the medical field usually have a metal needle mounted at the front of the barrel allowing for aspiration of fluid into the syringe and subsequent injection into the patient through the skin, or indirectly through a previously placed intravenous infusion line. Access to those lines is provided by a variety of devices called access ports. These access ports are primarily of two types, one with an intact septum or membrane and another which has been pre-slit to allow access by a completely blunt, usually plastic, cannula. Medication vials which do not have a pre-slit septum can be accessed by a blunt cannula using a separate valve or port which contains a pre-slit septum. This valve is inserted into and traverses the vial stopper allowing aspiration of the medication vial contents using a blunt cannula through the valve""s pre-slit septum. Therefore, health care workers must use either a sharp metal needle for aspirating medication vials or alternatively use an access port, to allow aspiration and injection using a blunt plastic cannula. The use of this blunt cannula for non-pre-slit septums requires an additional device, extra time, effort and cost. There is therefore a need for a cannula which has sufficient sharpness and/or other features, to allow penetration of a pre-slit septum or puncturing a non-pre-slit septum but which is not sharp or strong enough to accidentally or easily puncture the health care worker""s skin or a rubber glove protecting the hand. Such a cannula could be used for aspiration and injection through a variety of septums, membranes and other elastomeric stoppers without the need of additional access ports, spikes or other devices.
Additionally, after puncturing an access port in an IV line, the cannulas will be contaminated with fluid which may contain disease-causing viruses. Contact of this contaminated cannula with skin, damaged skin or mucous membrane can result in disease transmission. Also, during use of the cannula, the cannula, which has pierced a membrane, may be forced out of the membrane, e.g., if increased pressure is generated within a system, for example, by rapid injection of fluid. Alternatively, a full or partially filled syringe is sometimes left attached to the IV line by the needle inserted through a membrane, e.g., to allow titrating of additional aliquots of medication from the same syringe. The mechanical connection between a needle or plain cannula and an access port in an IV line is inevitably somewhat insecure.
In accordance with a preferred embodiment of the present invention, there is provided a cannula for a syringe which has (1) a piercing component or section for piercing non-pre-slit septums such as vial stoppers or entering pre-slit membranes, but which is sufficiently blunt to avoid penetration of a health care worker""s skin or surgical gloves; (2) a passage through the cannula with an axial opening to prevent lateral emission of fluids, when expressing fluid from a syringe as the accurate dose of medication is prepared as is common practice with needles and (3) discrete sections or components along the length of the cannula having different resistances, frictional or otherwise relative to a septum enabling a single cannula to be retained within a septum of different characteristics, e.g., thickness or hardness as a function of the extent of penetration of the cannula through the septum. To accomplish the first objective, the piercing section of the cannula, which is formed of a plastic material, is preferably smooth-sided, of relatively narrow diameter and has an inclined pointed surface or surfaces sufficient to penetrate both non-pre-slit and pre-slit septums. The cannula, however, has insufficient sharpness to easily or accidentally penetrate skin or surgical gloves (i.e., a supported flexible membrane. The tip of the piercing section preferably has a surface inclined approximately 20-45xc2x0 with the central passage opening axially through the surface. To facilitate penetration, a coating may be applied along the length of the piercing section, e.g., which may be approximately one-half inch in length. The coating may comprise a lubricious material, e.g., silicone, or a surface coating such as Parylene.
To provide a cannula having a variable resistance to movement relative to a septum, second and possibly third sections are spaced axially from the piercing section and away from the tip of the cannula. The second section is preferably of a larger diameter than the piercing section and the third section is preferably although not necessarily, of a larger diameter than the second. Thus, multiple sections of increased diameter in a direction axially away from the cannula tip are provided. The second section has mechanical formations, e.g., roughened or textured surfaces or barbs, ribs or indentations, or merely increased diameter to increase the frictional resistance to removal of the cannula from a septum. For example, for use with relatively thinner pre-slit septums, discrete projections may be formed on the second section to increase frictional resistance to withdrawing movement of the cannula from the thinner septum. The third and preferably larger diameter section is spaced axially further from the tip of the cannula from the septum. The latter may be used with thicker pre-slit septums or septums with a larger slit, i.e., the cannula would be inserted into the septum to a greater extent to locate this portion of the cannula with the higher coefficient of friction into engagement with the walls of the septum.
In another form hereof, portions of one or both of the second and third sections of the cannula, which preferably increase in diameter in a direction away from the tip of the cannula, have reduced diameter indentations or xe2x80x9cwaists.xe2x80x9d The change in diameter of the waists relative to remaining portions of the sections affords increased resistance to movement of the cannula relative to the septum. From the foregoing, it will be appreciated that the cannula may be inserted into various thicknesses or sizes of septums or septal slit and, depending upon the depth of insertion of the cannula, the resistance to removal of the cannula can be regulated. Thus, the present cannula mounted on a syringe can be positioned to resist pulling out of the septum to varying degrees. In addition to this feature, the cannula is also sufficiently sharp to pierce non-pre-slit septums, such as present on medication vials or evacuated containers for blood or other fluid collection. The cannula is, however, sufficiently blunt to substantially preclude accidental penetration through an individual""s skin or medical gloves.
Additionally, while the cannula has insufficient sharpness to easily penetrate an individual""s skin or surgical gloves, cannulas are contaminated after use with fluids and could, upon contact with mucous membranes, skin or damaged skin, facilitate the transmission of certain diseases. Consequently, the cannula is also configured for use with a retractable needle-type syringe in which the cannula can be retracted into the syringe barrel subsequent to use. Accordingly, the end of the cannula opposite the cannula tip may be formed in a number of different configurations such that the cannula can be coupled, e.g., by Luer-type connections with retractable needle-type syringes or be integral with syringe adapters used with other forms of retractable needle-type syringes to enable the cannula to be withdrawn into the syringe barrel. Thus, the opposite end of the cannula may have a Luer fit or Luer lock mechanism or be configured to mate with an adapter of a syringe for withdrawal into the syringe.
In a preferred embodiment according to the present invention, there is provided a cannula for use with a syringe and for insertion through a membrane, comprising an elongated sleeve formed of a plastic material and having a central axial passage therethrough for transmitting a fluid between opposite ends thereof, the sleeve terminating in a tip at one end with the passage opening axially through the tip, an opposite end of the sleeve adapted for connection with the syringe and means formed on an outer surface of the cannula at different axial locations therealong affording respective differential resistances to movement relative to the membrane as a function of the depth of penetration of the cannula relative to the membrane.
In a further preferred embodiment according to the present invention, there is provided a cannula for use with a syringe and for insertion through a membrane, comprising an elongated sleeve formed of a plastic material and having a central axial passage therethrough for transmitting a fluid between opposite ends thereof, the sleeve terminating in a tip at one end thereof, an opposite end of the sleeve adapted for connection with the syringe and mechanical formations on an outer surface of the cannula at different axial locations therealong affording respective differential resistances to movement relative to the membrane as a function of the depth of penetration of the cannula relative to the membrane.